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In practice, vector control methods are widely used offering the possibility to reach high performance. Certain application areas need optimum control in at limit operating conditions, as, operation at maximum torque. The paper presents how through the proposed control scheme at the output of the flux and the voltage controllers, provide direct the frequency and voltage values for an asynchronous machine (ASM) operating at variable speed. The simulation analyses for the considered control structure are based on the use of two controllers: flux regulator for determining the stator flux and the speed regulator for determining the stator frequency. The dynamic analysis of the system is done highlighting the tuning process for the two controllers, which enables conclusions on the proposed method with different applications, as the ASM in wind turbines.

This paper presents a control method for a wind turbine with a synchronous generator with permanent magnet (SGPM), to achieve optimal function in the optimal energy field at variable wind speed. The wind speed and the angular speed of the SGPM impose the value of the generator load in the optimal energy area. Based on energy balances, done with speed and power measurements, the generator load is determined so that the system can be brought into the optimal energy area. The operation at maximum power of a wind turbine (WT) is analyzed by modifying the generators load, under the terms of a significant wind speed variation in time. The coordinates of the maximum power point (MPP) change in time being determined by the instantaneous values of the wind speed and the mechanical inertia, not in every case the wind turbine can be brought, in a timely manner, in the MPP area. The rapidity of the wind speed variation in time as well as the inertial value, are two fundamental elements upon which the operation in MPP depends. Prescribing the value of the DC current, Icc, from the intermediate converter circuit, a simple and useful control of the wind turbine system can be achieved. The control method that allows the WT to function in the optimal energy area is based on knowing the value of Icc, which is determinate from wind speed and the angular mechanical velocity (AMV).

The modern, developed society becomes aware of the necessity to conserve and protect the environment, increasing the gained benefits from a rational use of the natural resources. The pollution and the limitation of the fossil fuels, associated with the political situation worldwide that affects direct the energy strategies, have opened opportunities in the area of operation renewable energy sources. The development of the exploitation of renewable energy sources is directly linked to the energy politic, which, in terms of Romania, has the focus to integrate into the European Union energy strategy. The year 2014 brought in Romania many legislative changes to the renewable support scheme, that proves, once again, the legislative unpredictability and limitations introduced by the legislator "during the game" that overthrew all economic profitability calculation of the existent and planned investments in this sector. The actual stage of the wind energy across Europe and the particular situation in Romania are highlighted; also a 2020 forecast for Romania tries to evaluate the perspective for the wind, and general, renewable energy market. The actual Romanian renewable energy support scheme, mainly regulated by "Law 220/2008" ends December 2016. The so-called "ready to build" projects especially wind- or hydropower, can't be finalized until this deadline, being unable to qualify to the existing, mainly to inoperable, support scheme. Another legislation that has to clarify how investments in renewable energy will be supported is still not in place, blocking any project development, implementation and economical benefit of the producer. The paper presents in this respect an updated overview of the Romanian renewable energy sector and its perspective.

Based on experimental measurements, this paper presents the vibration analysis of a hydro generator that equips a Kaplan hydraulic turbine of a Hydropower plant in Romania. This analysis means vibrations measurement to different operating regimes of the hydro generator respectively before installing it and into operation, namely putting off load mode (unexcited and excited) respectively putting on load mode. By comparing, through the experimental results obtained before and after the operation of hydro aggregates are observed vibrations improvements.

Vector control methods offer the possibility to gain high performance, being widely used. Certain applications require an optimum control in limit operating conditions, as, at maximum torque, that is not always satisfied. The paper presents how the voltage and the frequency for an asynchronous machine (ASM) operating at variable speed are determinate, with an accent on the method that keeps the rotor flux constant. The simulation analyses consider three load types: variable torque and speed, variable torque and constant speed, constant torque and variable speed. The final values of frequency and voltage are obtained through the proposed control schemes with one controller using the simulation language based on the Maple module. The dynamic analysis of the system is done for the case with P and PI controller and allows conclusions on the proposed method, which can have different applications, as the ASM in wind turbines.

This paper presents an intelligent system capable of eliminating the surface flaws and casting rejects, to increase the quality of continuously cast products and implicitly to increase the productivity of the installation.This method contains a fuzzy controller which requires changes of the water flow value at the secondary cooling. Fuzzy system controlling in real time the distribution of the water flow rate according to the real situation in the installation and working as an adaptive. The simulations results show us that the control strategy proposed is a very efficient method for the water flow control in the secondary cooling stage.

This paper presents an enhanced method that accurately identifies natural frequencies of structures, via an important improvement of spectral lines density. Spectral lines density increases due to the superposition of many spectra, each spectrum being accomplished by subtracting certain number of samples from the original signal and using the power spectral density analysis. The newly achieved overlapped-spectrum shows important additions to spectral line number and makes more accurately identification of frequencies in the peak position of relevant amplitudes. In this way, modal analysis becomes more reliable and efficient. Method application assumes small frequency changes and the advantage of establishing more precisely the position and dimension of damage. The analysis of all results explicitly indicates an important assessment in the evaluation of frequency. Considering relevant aspects, it can be appreciated that the approached method offers a new development way in the vibration-based damage detection, allowing de possibility to perform more accurate evaluation of frequencies and introducing new features into the domain.